Terpenes are a large class of organic compounds that are often naturally produced by plants and provide the fragrant aroma of plant-derived essential oils. Many terpenes and their associated essential oils are widely known to be pharmaceutically active. Because of this, people have developed various ways of administering terpenes to treat many different ailments.
By way of example, peppermint oil is widely used to address gastrointestinal problems such as irritable bowel syndrome because it inhibits the smooth muscles in the gastrointestinal tract from contracting. Unfortunately, however, if peppermint oil is released in the stomach, it is absorbed quickly and can upset the stomach. To overcome this problem, others have developed oral delayed-release peppermint oil formulations that allow the peppermint oil to pass into the intestines before it is released.
A common method for delivering peppermint oil to the intestines is to load a hollow capsule with peppermint oil and coat the capsule with an enteric coating. The enteric coating prevents the capsule from dissolving in the stomach and releasing the peppermint oil too early.
These single-unit enteric coated capsules have several drawbacks, including extremely variable gastric emptying time (from 60 to 570 minutes), dose dumping, and their inability to exit from the contracted pylorus due to the presence of food in the stomach. These problems can be addressed by developing multiparticulate compositions containing terpene-based active ingredients. In U.S. patent publication 2012/0207842 and corresponding WIPO publication WO 2012/109216, we described a multiparticulate formulation containing high-purity L-menthol. Some of the particulates in those formulations included a core containing L-menthol, a subcoating over the core, and an enteric coating over the subcoated core. The preferred subcoating was hydroxyl propyl methyl cellulose or “HPMC.” The multiparticulate formulations described in that application provided the release profile that we desired and worked well for some applications, but are not optimized for all applications. U.S. patent publication 2012/0207842 and WIPO publication WO 2012/109216 are both incorporated by reference in their entireties.
We found that it is difficult to make multiparticulate formulations containing terpene-based active ingredients because terpenes are very volatile. If the multiparticulate core containing terpene-based active ingredients is heated or stored for extended periods, much above room temperature, the terpenes will permeate, evaporate or sublimate and leave the core. This made processing the cores very difficult, especially when it came time to cure the enteric coating on the cores at elevated temperatures. For our L-menthol formulations, we resorted to low temperature processing techniques.